In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) communication is discussed as a new function after Release 12 (see non patent document).
In the D2D communication, a plurality of adjacent user terminals perform direct communication in a frequency band assigned to a mobile communication system. It is noted that the D2D communication is also called proximity service (Proximity Service) communication.